1. Field of the Invention
The present invention relates to an exposure apparatus, an exposure method, and a device manufacturing method for manufacturing electronic devices such as semiconductor devices, liquid crystal displays, image-capturing devices (such as a CCD), thin-film magnetic heads or the like.
2. Description of the Related Art
Projection exposure apparatuses are used in manufacturing electronic devices such as semiconductor devices and liquid crystal displays by using photolithography. This type of projection exposure apparatus projects the image of a pattern formed on a mask or reticle (hereinafter called xe2x80x9creticlexe2x80x9d) on projection (shot) areas on a substrate whose surface is coated with a photosensitive agent (resist) via a projection optical system. The circuit of the electronic device is formed by transferring circuit pattern on the substrate by using the projection exposure apparatus, and by post-processing. An integrated circuit comprises, for example, approximately twenty layers of such circuit interconnections provided repeatedly.
Due to recent high-intensity integration of integrated circuits (i.e. miniaturization of circuit patterns), the wavelengths of illumination light for exposure (hereinafter called xe2x80x9cexposure lightxe2x80x9d) in the projection exposure apparatus are becoming shorter. In other words, exposure apparatuses that use a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (193 nm) are nearing the final stage of practical use. In the quest for even higher-intensity integration, research is being made into an F2 laser (157 nm) and an Ar2 laser (126 nm).
Light (energy beam) having a wavelength of approximately 120 nm to 200 nm belongs in the vacuum ultraviolet region, and such light (hereinafter called xe2x80x9cvacuum ultraviolet raysxe2x80x9d) does not pass through air. This is due to the act that substances such as oxygen molecules, water molecules, and carbon dioxide molecules (hereinafter called xe2x80x9clight-absorptive substancexe2x80x9d) in the air absorb the energy of the light.
For this reason, when the vacuum ultraviolet rays are used as the exposure light, the light-absorptive substance in the space on the path of the exposure light must be reduced in order to enable the exposure light to attain a sufficient level of illumination on the substrate. Therefore, in conventional exposure apparatuses, the light-absorptive substance in the light path space is reduced by maintaining the space in a state of reduced pressure, and replacing the gas in the space with a supply of a gas (low absorptive gas) which has low absorption of energy of exposure light after reducing the pressure of the space.
For instance, in an exposure apparatus using the F2 laser, the entire space on the path of the exposure light beam must be purged with a high-purity inert gas. In this case, when the total light wavelength is for example 1000 nm, the density of the light-absorptive substance on the optical path should for practical purposes be less than approximately 1 ppm.
However, a reticle generally has a protection member called a pellicle in order to prevent unwanted substances from adhering to the pattern formation areas, and the pellicle is usually fixed to the reticle via a frame (metal frame). Consequently, when the vacuum ultraviolet rays are used as the exposure light as described above, it is also necessary to reduce a light-absorptive substance in the space (space inside pellicle) created by the pellicle and the metal frame.
The frame usually comprises an opening (ventilation hole) for preventing the pellicle from breaking when the atmospheric pressure changes. The opening prevents the pellicle being broken without creating any difference between the pressure in the space in the pellicle and the atmospheric pressure, even when the atmospheric pressure changes as a result of, for example, transportation by aircraft, a change in weather or the like.
The pellicle is an extremely thin transparent film having a thickness of approximately several hundred nanometers to several micrometers, and has an organic compound such as nitrocellulose as its essential component. Therefore, in the aforementioned method for reducing pressure in the space, there is a danger that the pellicle will deform and break as a result of changes in the pressure in the space, making it difficult to stably reduce the light-absorptive substance.
The present invention has been achieved in order to solve the above problems. It is an object of the present invention to provide an exposure method and apparatus, and a device manufacturing method, which can stably and efficiently reduce a light-absorptive substance from the space formed by a pellicle in a reticle, and increase the precision of the exposure light.
In order to achieve the above objects, a first aspect of the present invention provides an exposure apparatus comprising a mask having a first space formed by a protection member, which protects a pattern formation area on a mask substrate, and a frame, which supports the protection member, inside a second space, the pattern of the mask provided in the second space being transferred onto a substrate by using an energy beam from a light source. The exposure apparatus has a gas replacement chamber which replaces gas in the first space with a predetermined gas, which the energy beam passes through, while maintaining a predetermined pressure in the first space.
In this exposure apparatus, the gas replacement chamber replaces the gas in the first space, formed by the protection member and the frame, with the predetermined gas while maintaining a predetermined pressure in the first space. Deforming of the protection member due to pressure change is thereby reduced, and breakage of the protection member is prevented. Therefore, the light-absorptive substance is stably reduced from the first space.
In this case, a gas supply device which supplies the predetermined gas to the gas replacement chamber may be provided, and the frame may have a supply opening, which supplies the predetermined gas in the gas replacement chamber to the space, and an exhaust opening, which exhausts the gas in the space into the gas replacement chamber. The gas supply device supplies the predetermined gas to the gas replacement chamber, and the flow of gas in the gas replacement chamber at this time causes the predetermined gas to be supplied via the supply opening in the frame to the first space, and causes the gas in the first space to be exhausted via the exhaust opening.
An exhaust device may be provided in order to exhaust the gas, exhausted from the first space to the gas replacement chamber, thereby shortening the time taken to replace the gas.
The supply opening of the frame and the supply opening of the gas supply device may be provided opposite each other. Furthermore, the exhaust opening of the frame and the exhaust opening of the gas exhaust device may be provided opposite each other. In this case, the predetermined gas, which has flowed through the supply opening of the gas supply device, maintains an approximately steady fluidity as it flows from the supply opening of the frame to the first space, and gas flows out from the exhaust opening in the first space.
The gas replacement chamber may comprise a gas supply device having a supply nozzle connected to the supply opening in the frame, and a gas exhaust device having an exhaust nozzle connected to the exhaust opening in the frame. In this case, the gas supply nozzle leads the predetermined gas, supplied from the gas supply device, via the supply opening in the frame directly to the first space. In addition, the gas exhaust nozzle leads the gas in the first space via the exhaust opening in the frame directly to the gas replacement mechanism. Consequently, little of the predetermined gas is wasted when replacing gas in the first space.
The gas replacement chamber may be equipped with a detection device which detects pressure change in the first space, and a control device which maintains the pressure in the first space at a predetermined pressure by controlling at least one of the gas supply device and the gas exhaust device based on a detection result of the detection device. In this case, since the control device maintains the pressure of the first space at a predetermine ed pressure based on a detection result of the detection device, breakage of the protection member can be reliably prevented.
The detection device may comprise a displacement sensor which detects displacement of the protection member, whereby pressure change of the first space can easily be detected from the outside.
The gas replacement chamber may be equipped with an optical cleaning device which cleans at least one of the mask and the protection member. Since the optical cleaning device decomposes by oxidization the light-absorptive substance which has adhered to the protection member and the mask, the exposure light reliably passes the mask having the protection member.
Another aspect of the present invention provides an exposure method comprising providing a mask having a first space formed by a protection member, which protects a pattern formation area on a mask substrate, and a frame, which supports the protection member, inside a second space, and transferring the pattern of the mask provided in the second space onto a substrate by using an energy beam from a light source. The gas in the first space is replaced with a predetermined gas, through which the energy beam can pass, while maintaining a predetermined pressure in the first space.
This exposure method replaces the gas in the first space, formed by the protection member and the frame, with the predetermined gas while maintaining a predetermined pressure in the first space. Therefore, deforming of the protection member due to pressure change is reduced, and breakage of the protection member is prevented.
Another aspect of the present invention provides a device manufacturing method using a photolithography process. In the photolithography process, the device is manufactured by using the exposure method apparatus mentioned above.
In this device manufacturing method, the device is manufactured by using the exposure method apparatus according to the present invention described above. Therefore, the substrate is illuminated by exposure light having a sufficient luminance, increasing the precision of the pattern of the device.
Another aspect of the present invention provides an exposure method using a mask having a first space formed by a protection member, which protects a pattern formation area on a mask substrate, and a frame, which supports the protection member, and transfers the pattern of the mask onto a substrate by using a beam from a light source. The method comprises accommodating the mask in a second space, to which a transparent gas through which the beam can pass is supplied, moving the mask in a predetermined direction inside the second space, and feeding the gas into the first space via an opening (or openings) formed in the frame.
In this exposure method, the movement of the mask feeds the gas, which the beam from the light source passes through, via the opening provided in the frame to the first space of the mask. The flow of the gas reduces the light-absorptive substance in the first space. Therefore, the beam from the light source reaches the substrate with a sufficient luminance, increasing the exposure precision.
A plurality of openings may be formed facing each other in the frame. The predetermined direction may comprise the direction which the plurality of openings are facing. In this case, the gas flows smoothly through the plurality of openings to the first space.
The exposure method for transferring the pattern of the mask to the substrate may comprise a scanning exposure method wherein the mask and the substrate are moved in synchrony. The predetermined direction may comprise the direction of the scanning. In this case, by scanning the mask, the gas can be fed smoothly to the first space.
By moving the mask in the predetermined direction inside the second space and replacing the gas in the first space with the predetermined gas prior to transferring the pattern of the mask to the substrate, the beam from the light source can reach the substrate with a sufficient luminance.
The second space may be an internal space of the mask chamber, which the mask is accommodated in when transferring the pattern of the mask to the substrate. By moving the mask in the predetermined direction inside the mask chamber when transferring the pattern of the mask to the substrate, the gas may be fed to the first space. This reduces the light-absorptive substance in the first space during transferring of the pattern of the mask, and maintains the reduction of the light-absorptive substance in the first space. The light-absorptive substance exhausted from the first space enters the second space, and may absorb light. However, a high-purity purge gas is fed into the second space to prevent buildup therein, and enabling the gas to be exhausted easily.
The second space may be an internal space of the mask chamber, which the mask is accommodated in when transferring the pattern of the mask to the substrate. When exchanging the substrate with another substrate, the mask may be moved in the predetermined direction inside the mask chamber so as to feed the gas into the first space. During substrate exchange, the light-absorptive substance in the first space is reduced and is maintained in this reduced state.
The second space may be provided separately from the mask chamber, which the mask is accommodated in at the time of transferring the pattern of the mask to the substrate, and may comprise an internal space of a preparation chamber, which the mask to be accommodated in the mask chamber is temporarily accommodated in. This makes it possible to accommodate the mask, which has reduced light-absorptive substance in its first space land is accommodated in the preparation chamber, in the mask chamber.
In this case, another mask, which is separate to the mask accommodated in the mask chamber, may be moved in the predetermined direction in the preparation chamber while feeding the gas into the first space of the mask. The mask in the mask chamber can thereby be speedily exchanged with the mask having reduced light-absorptive substance in its first space.
The protection member and/or the mask in the second space may be optically cleaned. The light-absorptive substance which has adhered to the mask and/or the protection member is decomposed by oxidization and discharged into the gas.
It is acceptable to detect information relating to the density of impurities in the first space, and to move the mask in the second space in the predetermined direction based on the detection result. In this case, the density of impurities (light-absorptive substance) in the first space can be reliably reduced.